Chemically, cefpodoxime proxetil is 1-isopropoxycarbonyloxyethyl(6R, 7R)-7-[2-(2-aminothiazol-4-yl)-2-(Z)-(methoxyimino)acetamido]-3-(methoxymethyl)-3-cephem-4-carboxylate of Formula I and is disclosed in U.S. Pat. No. 4,486,425.

Cefpodoxime proxetil is one of the limited class of third generation cephalosporin derivatives which can be administered orally as it is readily adsorbed through the digestive tract and which is then readily hydrolyzed and converted in vivo to the corresponding carboxylic acid which, in turn, shows outstanding antibacterial activity against both gram-positive and gram-negative bacteria.
Pharmaceutical compounds are required in highly pure form because of the fear of unknown and potentially harmful effects of impurities. For purposes of patient' safety, it is highly desirable to limit the amount of impurities present in any medicament administered to a patient. This is achieved by either devising a process for or by additional purification steps like chromatography or recrystallization etc. The purity of intermediates and raw materials is essential for obtaining the target pharmaceutical compounds in high yield and purity.
A number of methods have been outlined in U.S. Pat. No. 4,486,425 for the synthesis of the cefpodoxime esters. However, in each of these methods, esterification of the carboxylic acids of the cephem ring results in impurities which have to be removed using silica gel column chromatography, as illustrated in the examples. U.S. Pat. Nos. 4,482,710 and 5,461,043 also illustrate the synthesis of cefpodoxime proxetil using methods outlined in U.S. Pat. No. 4,486,425 which employ chromatography after the esterification step to remove impurities and to get pure cefpodoxime proxetil.
PCT application WO 99/35149 describes the preparation of cefpodoxime proxetil with a focus on the adjustment of diastereoisomeric ratio of the two diastereoisomers of cefpodoxime proxetil in the product mixture. Although, the process illustrated in this PCT application does not use chromatographic techniques for isolation of products, the process involves additional steps of protection and deprotection at the amino position of the thiazolyl moiety.
Thus none of the prior art processes are satisfactory for the reasons described above.